Electrolytic separation of metals

An interesting application of these results is to the direct quantitative separation of copper and cadmium. The copper is first deposited in acid solution the solution is then made slightly alkaline with pure aqueous sodium hydroxide, potassium cyanide is added until the initial precipitate just re-dissolves, and the cadmium is deposited electrolytically. 

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ELECTROLYTIC SEPARATION OF METALS WITH CONTROLLED CATHODE POTENTIAL 12.6... 

Electrolytic separation of metals 508, 509 of cobalt and nickel, (cm) 533 with controlled cathode potential, 517, 518 see also under individual metals Electromagnetic radiation 646 Electron as standard reagent 535 Electron capture detector 242... 

The electrolytic separation of metals from waste solutions is therefore problematic as these solutions are usually dilute in metal ion. 

When a sample is dissolved, the phosphorus usually passes into solution as P(V). Rather than isolate the phosphate, it is often better to isolate the interfering elements, leaving the phosphate to be determined in the mother liquor. Examples of such separations include distillation of Si, As, and Ge as volatile halides [1] or of boron as trimethyl borate [2], precipitation of heavy metals as sulphides from an acid medium, retention of cations on a strongly acidic cation exchanger, and electrolytic separation of metals. 

When the copper content in the Dorn metal has been reduced to less than 1% by fire refining, the metal is cast into anodes for electrolytic separation of silver. A typical analysis of Dorn metal is... 

It may be noted that the statement made above—that the surface potential in the electrolyte phase does not depend on the orientation of the crystal face—is necessarily an assumption, as is the neglect of S s1- It is another example of separation of metal and electrolyte contributions to a property of the interface, which can only be done theoretically. In fact, a recent article29 has discussed the influence of the atomic structure of the metal surface for solid metals on the water dipoles of the compact layer. Different crystal faces can allow different degrees of interpenetration of species of the electrolyte and the metal surface layer. Nonuniformities in the directions parallel to the surface may be reflected in the results of capacitance measurements, as well as optical measurements. 

After reviewing the properties and structure of ionic liquids, leading specialists explore the role of these materials in optical, electrochemical, and biochemical sensor technology. The book then examines ionic liquids in gas, liquid, and countercurrent chromatography, along with their use as electrolyte additives in capillary electrophoresis. It also discusses gas solubilities and measurement techniques, liquid-liquid extraction, and the separation of metal ions. The final chapters cover molecular, Raman, nuclear magnetic resonance, and mass spectroscopies. 

Bunsen is remembered chiefly for his invention of die laboratory burner umned after him. He engaged in a wide range of industrial and chemical research, including blast-furnace firing, electrolytic cells, separation of metals by electric current, spectroscopic techniques (with Kirchhoff). and production of light metals by electrical decomposition of their molten chlorides. He also discovered two elements, rubidium and cesium. 

The above techniques that involve high-temperature processes are known as pyromet-allurgy. Another common technique involves the electrolytic reduction of metal compounds, often referred to as hydrometallurgy or electrorefining, depending on whether the procedure is carried out before or after the metal has already been separated from its ore, respectively. 

One of the most remarkable and useful properties of fully dissociated strong-base anion exchangers is their unique tendency to interact selectively with metal ions that are complexed by the exchanger counterions. When metal ion is added to the electrolyte solution equilibrated with the exchanger a portion of the absorption spectrum resolved for the exchanger phase is not matched by the absorption spectrum of the solution phase even when care has been taken to keep the concentration level of counterion in the two phases the same. Advantage of this property has been taken for the development of a number of anion-exchange facilitated separations of metals [6,7,20]. 

Mercuiy cathode separations at constant current, although not suitable for electrogravimetric determinations, often are useful as adjuncts to other analytical methods. Casto ° summarized various procedures for the electrolytic removal of metallic impurities from uranium. 

Electroplating, Etc.—The energy required for electroplating, galvanoplasty, detinning and electrolytic refining of metals varies with the metals involved and solutions used. From 1 to 100 amp. may be needed per square inch of cathode surface, at 0.1 to 4 volts per cell. Direct current is supplied from small generators at 5 or 6 volts, and a separate rheostat is required for each cell or tank. 

The largest group of elements comprises those isolated from solution in the elemental form as a result of reduction, usually electrochemical. In acid solution, the electrolytic deposition of metal on a solid cathode is limited to noble and semi-noble metals. Trace analysis of copper and its compounds may serve as an example [100]. An anodic dissolution technique may be applied for the isolation of macroscopic amounts of copper. A sample in the form of a bar, plate, or wire is the anode in the electrolytic system. When current is passed through the electrolyte (nitric acid + persulphate), Cu is deposited on the graphite cathode, while most trace elements accumulate in the solution. In the trace analysis of platinum, the matrix has been also separated on a cathode [101]. 

Y. Shi and J. S. Fritz, Separation of metal ions by capillary electrophoresis with a complexing electrolyte,. 1. Chromatogr., 640, 473,1993. 

Preliminary studies have shown that ionic liquids have potential as solvents and electrolytes for metal recovery, and the feasibility of these solvents has been demonstrated for the extraction of gold and silver from a mineral matrix [7], the recovery of uranium and plutonium from spent nuclear fuel [8], and the electrodeposition and electrowinning of metals (especially, for active metals such as Li, Na, Al, Mg, and Ti) from ionic liquids [9-11], Ionic liquids as green solvents and electrolytes have shown important and potential application in extraction and separation of metals. In this chapter, the new applications and the important fundamental and appUed studies on the extraction and separation of metal in ionic liquids including metal oxides and minerals or ores processing, electrodeposition of metals (mainly for active metals), and extraction and separation of metal ions are described. 

Figure 8.11. Separation of metals by capillary electrophoresis on a 60 cm x 75 pm I.D. fused-silica capillary column at 20°C with a potential of 30 kV. The electrolyte solution contained 15 mM lactic acid, 8 tuM 4-methylbenzylamine and 5 % (v/v) methanol at pH 4.25. (From ref. [415] Elsevier).

Recovery of valuable metals from secondary sources. At the present state of development the more promising metal recovery processes based on SIR systems appear to be in the following applications in terms of both process performance and economic considerations (a) Recovery of metals from dilute solutions, particularly where such solutions are available at low cost (e.g., waste solution from other processes, mine waters, or dump leaching solutions) (b) separation of metals from concentrated solutions obtained by hydrometallurgical processing of complex ores, concentrates, mattes, and scraps and purification of process solutions (such as electrolytes) which may contain a variety of metals that have been only partially recovered in the conventional processing steps (c) separation and purification of met-... 

Lactic acid makes possible the separation of metal ions with almost identical mobilities by complexing the individual metal ions to varying degrees. However, NH andK" " cations also have virtually identical mobilities and are not complexed by lactic acid. Potassium ions can be separated by CZE if a suitable crown ether is incorporated into the electrolyte [15-18]. The K ion is selectivity complexed and its mobility is reduced just enough to permit a good separation. 

Lopez-Cacicedo CL. The electrolytic recovery of metals from diluent elBuent streams. J Separ Proc Technol 2(1) 34—39,... 

Since a potassium electrolyte has better conductivity but separation of metallic potassium from the amalgam is difficult, a method for regeneration of potassium-containing electrolytes has been developed on the basis of the reaction of the potassium amalgam with NaAlR4 [57, 102]. Use of this double-decomposition reaction has made it possible to develop a scheme for the preparation of tetraethyllead with complete regeneration of the electrolyte ... 

Electrochemical methods. Hie electrolysis of dilute sulfuric acid solutions with a mercury cathode results In the quantitative deposition of Cr, Fe, Co, Nl, Cu, Zn, Qa, Oe, Mo, Rh, Pd, Ag, Cd, In, Sn, Re, Ir, Pt, Au, Hg, and T1 In the cathode. i Arsenic, selenium, tellurium, osmium, and lead are quantitatively separated from the electrolyte, but are not quantitatively deposited In the cathode. Manganese, ruthenium, and antimony are Incompletely separated. Uranium and the remaining actinide elements, rare earth elements, the alkali and alkaline eeu th metals, aluminum, vanadium, zirconium, niobium, etc. remain In solution.Casto and Rodden and Warf— have reviewed the effects of many variables In the electrolytic separation of the above-named elements from uranium. According to Rodden and Warf optimum conditions for the purification of uranium In sulfuric acid solutions with a mercury cathode are electrolyte volume,... 

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